To meet a continuously increasing demand for wireless data traffic, wireless communication systems are advancing to supporting a higher data rate. A 4th Generation (4G) system currently commercialized mostly seeks to enhance spectral efficiency in order to increase the data rate. However, it is not easy to meet the sharply increasing demand for the wireless data traffic merely with spectral efficiency enhancements.
One solution for meeting the wireless data traffic demand uses a very wide frequency band. Since current mobile communication cellular systems generally use the frequency band below 10 GHz, it is quite difficult to secure the wide frequency band. Hence, it is necessary to secure broadband frequencies in the higher frequency band. For example, introduction of a millimeter wave (mm wave) system is under discussion to secure the wide frequency band. However, as the frequency for the wireless communication increases, a propagation path loss also increases. As a result, a propagation distance is relatively shortened and service coverage shrinks. Key techniques for mitigating the propagation path loss and extending the propagation distance include a beamforming technique.
A conventional cellular system uses Channel Quality Information (CQI) for scheduling. The CQI is feedback information provided by a mobile station to a base station by measuring receive channel quality. For example, the CQI includes a Signal to Interference plus Noise Ratio (SINR). It is appropriate to use the CQI of the SINR type as the scheduling information when a dynamic range of the receive signal strength and an interference signal strength is not considerable. However, in wireless communication systems using beamforming, it is inadequate to use the CQI of the SINR type measured by the mobile station as the feedback information for the scheduling because the dynamic range of the receive signal strength and the interference signal strength is considerable based on TX/RX beamforming. Thus, what is needed is adequate CQI as the feedback information for the scheduling in the wireless communication system using beamforming.